When using a userspace stack you can (and should!) optimize your program during and after link to put hot code together on same/nearby lines and pages. You cann

When using a userspace stack you can (and should!) optimize your program during and after link to put hot code together on same/nearby lines and pages. You cannot do this or anything approximating this between an application and the Linux kernel. When Linux is built the linker doesn't know which parts of its sprawling network stack are hot or cold.